Advanced French Fighters vs 1942/1943 contemporaries

bf109xxl said:

Any reference on primary sources would be appreciated - for both statements ("some pilots preferred" and "12.7 penetrated better").
After reading many memoirs and interviews of Soviet fighter pilots, I got the impression that they were quite satisfied with the ShVAK, and only very rarely was there an opinion that it would be better to put another UB instead of the ShVAK, but the reason was not the worse penetration, but the ammunition. At the same time, many pilots stated that they rarely used the entire ammunition of the ShVAK in aerial combat.

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There was a variety of ammunition for both guns, with different target effects. A pilot's impression could depend on the ammo his guns were loaded with.

But if we are comparing AP to AP for the two rounds the 20mm is going to come off worse. The 20mm is trying to blow a hole just under 2 1/2 times the size (area) and it has just under 2 times the energy of 12.7mm to do it. That is at the muzzle. The 20mm projectile in the ShVAK cannon is not the best. It is a little light for the bore size (sectional density) and doesn't have a very good shape, Most 20mm projectiles (anybody's) are not well shaped compared to the US and Soviet 12.7mm projectiles.

HE projectiles (anybody's) usually don't penetrate well, unless the fuse fails.
12.7mm US and Soviet projectiles were very seldom HE or even holding much incendiary material. Usually about 2 grams of material in the nose ahead of the AP core, useful for indicating impact.

I have no primary sources.
It does seem that some of figures used in old western books for velocities for the Soviet guns were a little off, or modern sources are down playing them for some reason.

It is a little hard to get around physics. Soviet 20mm ammo used projectiles of around 93-99 grams? Hispano's used about 127-130 grams ( there may be a bit more variation?) but at the same speeds the AP round (full bore, not using sub caliber tungsten penetrators) is going to penetrate about 25-30% more than the ShVAK round. There was/is no magic. People had been figuring out how to get through iron/steel plates since about 1860. By 1940 they had a pretty good idea of what worked in full bore ammunition for steel types and heat treatments. Doesn't mean some countries used the best option/s at times (British 2pdr).

There are accounts of British pilots not being happy with the early 20mm Hispano cannon due to lack of "penetration". In this case it was that the fuses detonated too early, on the skin of the aircraft and did not get inside where the crew/important stuff was. British had few/no 12.7mm guns and resorted to using inert/training rounds mixed into the belts/drums until the fuses were fixed/replaced. A 128 gram lump of steel could 'penetrate' quite a bit of aircraft structure if it didn't hit good armor or something like an engine.

TM06 said:

I'm not entirely sure about the amount of filler the HE (HEF-T?) had, I was able to find some documents around the internet but my Swedish isn't good enough to make sense of them. The most I could glean was a cartridge weight of 42 grams and 1~2 grams of explosive filler seems like a reasonable estimate for that.

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Some of the 'smaller' 12.7/13mm projectiles would hold 1-2 grams of explosive filler. If somebody had designed an HE bullet I would expect a bit more. Unfortunately for the Italians and Japanese they tended to put tracer elements on/in the back of the HE projectiles which took up space/volume and cut into the HE/incendiary payload.

TM06 said:

Regardless, it is still a very powerful gun and the HE would likely help at tearing through wings or tails with a well-aimed burst.

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It may not do what you think. There was an American pilot who's plane took several 20mm hits. One hit his port aileron and detonated in the aileron, damage was not as impressive as many would think. Not sure if it did much to aileron support spar. They recovered the back part of the shell from inside the aileron and the pilot had it bored out and ring made out of it, which tell use that it was NOT a mine shell and most likely a HET round that had around 5 grams of HE. Enough to burst the front of the shell but the rear ring of shell was pretty much intact. Perhaps the explosive was defective?

TM06 said:

Personally, I'd go with 2 x 13.2 mm per wing for any fighter with less than 3 cannons.

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Problem here is weight. Even the Belgian gun was as heavy as three 7.5mm machine guns. And the big MG ammo was about 5 times heavier, 200 rounds of 12.7/13.2 mm is as heavy as 1000 rounds of 7.5mm.
There is no sense to making a one 20mm and four 13.2mm fighter, you might as well just use the three 20mm guns.

TM06 said:

Weight might be an issue, but if they could lighten the Hispanos (which seems highly likely due to the very light weight of the 405 - weight saving methods could likely be transferred over to the 404 or a hypothetical 406) it probably wouldn't be too heavy.

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I have told you before how they lightened the 405 gun. They cut the hell out of the gun to take a much shorter shell.
British cut 8kg out of the 404 to make the MK V version. That included cutting 30cm off the barrel. You can cut all kinds of stuff if you are using a shorter, lower powered round.
Kind of like how you can lighted a rifle when you go from a 7.62X51 NATO to a 7.62X39 Soviet round.
Not sure if they even built the 405 gun.
And again, the only way to get light weight guns is to accept semi-disposable ones. Change the barrels and a few other parts and if they make it to 2,000-3,000 rounds fired then trash the gun and replace it. It won't be worth rebuilding.

Luft.4 said:

I am not understanding your first quote, C3 was a high octane fuel.

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You are absolutely right - it is high-octane gasoline, but only when large amounts of TEL (5.5 ml/l) were added. "Real" high-octane gasoline had a higher ON of the hydrocarbon base, and the addition of TEL was just about 0.8-1 ml/l.

Luft.4 said:

On par with US 100/130 grade, some test even state close to US 100/150 grade. Am I misunderstanding you?

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C3 was comparable or even superior to US 100 octane gasoline only on rich mixtures.

Luft.4 said:

I know of at least 3 Soviet oil fields that were used: Baku, Grozny and Ufimskoye.

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What you labeled as "Ufimskoye" is actually called "Volga-Ural petroleum province", a huge area with many oil fields.

Luft.4 said:

These are openly listed in aircraft engine manuals so they were used for aviation gasoline production.

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Bashkir oil was much worse than Baku oil - it was much more complicated to produce aviation gasoline from it, about 80% of Soviet aviation gasoline was produced from Baku oil. I can cite sources, but they are in Russian, unlikely to be interesting to you. Even gasoline produced in Grozny was considered much worse than the one from Baku.

Luft.4 said:

There is excellent information on the Luftwaffe's oil situation found in BaMA RL 2-VI 115 pages 2-3. If you wish to read on this subject in English, Calum Douglas wrote on this as well in his book The Secret Horsepower Race.

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The German source does not clearly answer the question:

Der Flugkraftstoffbestand betrug bei Kriegsbeginn, also im September 1939, etwa
400.000 to.
Er erhöhte sich bis Ende 1940 durch Beute, hauptsächlich aus französischen Beständen, auf rund
600,000 to.
Diese Menge setzte sich zusammen aus:
Reinbenzin, also nichtethylisiertem Grundbenzin
A 3, Oktanzahl 80
B 4, Oktanzahl 87-89
C 3, Oktanzahl 100
Der für die Luftwaffe am meisten infrage kommende Flugkraftstoff war das B 4.

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Thus, no specific information about what kind of gasoline was captured and what exactly it was used for was given. And further:

Mit Kriegsausbruch fielen die ausländischen Flugkraftstofflieferungen, bis auf die rumänischen Lieferungen, fort. Da Rumänien monatlich nur rund 6000–9000 to Flugkraftstoff lieferte, war die deutsche Luftwaffe grundsätzlich nur auf die heimische Erzeugung angewiesen.

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There is even less information on this topic in the book by C. Douglas. However, I may have missed or forgotten something important, I would be grateful if you could remind me of the page number.
An unambiguous answer was found here:

The aviation fuel was particularly valuable to the Germans at this time. According to Ahrens this comprised 160,000 tons captured in France and 80,000 tons captured in Holland. All the operations of the Luftwaffe against Great Britain in the summer and winter of 1940 were made on this fuel. (A.D.I.(X) 399/1945.)

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It was a bit odd to me because the results of the fuel analysis from the damaged German planes that landed in Britain didn't mention either French or Dutch gasoline, IIRC, and the physical and chemical properties of French gasoline were quite different as compared to the German one at close ON. Unfortunately memory sometimes fails, I'll have to go through the tables again - I'd be grateful if someone could tell me if there is any indication of French/Dutch origin of gasoline in the reports, so I don't waste my time if none is found.

Anyway, thanks for the references!

bf109xxl said:

Bashkir oil was much worse than Baku oil - it was much more complicated to produce aviation gasoline from it, about 80% of Soviet aviation gasoline was produced from Baku oil. I

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You may be well aware of it but the US oil varied considerably from east to west. East coast (Pennsylvania) was good for about 38-40 octane gas using WW I methods of refining.
West Coast oil could make about 70 octane gas with the WW I Methods, Texas/Oklahoma was somewhere in between, like 50-60?
Better refining methods changed things but it was always going to be easier/cheaper to use west coast or imported oil than east coast oil.

As you know there is a limit as to how much TEL can be used without increasing problems.


I have wondered if the German reluctance to use rich mixtures was due to trying to economize on fuel or if the injector systems wouldn't meter enough fuel or if the rich mixture didn't work as well with the fuel injection? The Fuel doesn't have much time to cool the mixture/absorb heat coming out of the direct injection nozzles? Or several reason put together?

Shortround6 said:

Some of the 'smaller' 12.7/13mm projectiles would hold 1-2 grams of explosive filler. If somebody had designed an HE bullet I would expect a bit more.

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How much more are we talking here? 5 grams? 10 grams? Half the bullet weight in filler?

Shortround6 said:

There is no sense to making a one 20mm and four 13.2mm fighter, you might as well just use the three 20mm guns.

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Perhaps there's a shortage in cannon production? Maybe the extra endurance of the 13.2's are more appealing? A five gun setup like that isn't entirely out of the picture, again look at some Italian designs. That's also the layout the SAAB 21 used as well, so it's at the very least worth considering.

Shortround6 said:

I have told you before how they lightened the 405 gun. They cut the hell out of the gun to take a much shorter shell.
British cut 8kg out of the 404 to make the MK V version. That included cutting 30cm off the barrel. You can cut all kinds of stuff if you are using a shorter, lower powered round.
Kind of like how you can lighted a rifle when you go from a 7.62X51 NATO to a 7.62X39 Soviet round.
Not sure if they even built the 405 gun.
And again, the only way to get light weight guns is to accept semi-disposable ones. Change the barrels and a few other parts and if they make it to 2,000-3,000 rounds fired then trash the gun and replace it. It won't be worth rebuilding.

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The example I used of the 405 is more about the potential to lighten the basic Hispano instead of the 405 itself. Although I do think the 405 could be a reasonable offensive gun, a lighter 404 or some derivative is more probable and would likely show up earlier than the British Mk V.

Shortround6 said:

Better refining methods changed things

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I have already mentioned the technological backwardness of the Soviet oil refining industry. New refineries equipped with American machinery under the Lend-Lease program only started to be built in 1943 and began production after the war. The USSR attempted to create a "Second Baku" in the Volga-Ural region, but this resulted in a largely inefficient use of funds and lower production volumes. Bashkir oil contains a lot of sulfur and paraffins and requires more complex refining methods involving additional steps. The USSR did not have its own version of a catalytic cracking process similar to the Houdry process.

Shortround6 said:

As you know there is a limit as to how much TEL can be used without increasing problems.

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Soviet engines that ran on gasoline with a high TEL content regularly had problems with spark plug reliability.

Shortround6 said:

I have wondered if the German reluctance to use rich mixtures was due to trying to economize on fuel or if the injector systems wouldn't meter enough fuel or if the rich mixture didn't work as well with the fuel injection? The Fuel doesn't have much time to cool the mixture/absorb heat coming out of the direct injection nozzles? Or several reason put together?

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The Germans wanted to use rich mixtures, they knew about their advantages. The problem was the dilution of oil with gasoline - the fuel didn't evaporate fast enough. They tried to fix that - the C3 in 1940 and in 1943 were different. A detailed consideration of the problems with the German fuel can be found in the book "The Secret Horsepower Race: Western Fighter Engine Development" by C. Douglas:

The C3 fuel of 1943 would evaporate more completely at a lower temperature than the C3 used in 1940, specifically to cure the oil dilution which had ruined the effectiveness of the DB 601 N engine in 1940 and 1941. Only the German engineers knew this however, and so the British were left to guess:

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TM06 said:

How much more are we talking here? 5 grams? 10 grams? Half the bullet weight in filler?

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Unless you do something really, really tricky with shell design and fabrication, like the German Mine shell, high velocity HE shells carried about 10% explosives to weight. Give or take a few percent.
Depends on the velocity range of the projectile and strength/quality of the steel. Lower velocity shells can use thinner walls with more volume for payload. Higher quality steel can allow for thinner walls.
However you can't quite scale a 20mm design down to 13mm exactly. The wall thickness has to stand up to the firing stresses or the shell may buckle while firing. There is also the problem of keeping the shell together in flight due to centrifugal force. A gun with a velocity of 800m/s and a 1 in 400mm twist is going to spin the bullet at 2000rps. Not 2000rpm but 2000rps which is 120,000rpm. You want the shells to reach the target and not disintegrate after leaving the muzzle. The wall thickness in greater in proportion than the 20mm or larger shell. Note that an 700m/s gun has less of a problem? There is also a problem with the fuses. The 13mm fuse can be a little smaller but not scaled exactly in proportion.
The US M23 incendiary bullet (no fuse) .50 cal bullet that was used for troop trials at the end of the war contained 5.8 grams of incendiary in a 32.4 gram bullet instead of the 43-46 gram projectiles. HE and Incendiary material are a lot less dense than steel or copper and light weight bullets are going to have rather different flight characteristics than the other projectiles (different aiming point). Basically you are going to max out at around 3 grams of filler for 13mm projectile.

TM06 said:

A five gun setup like that isn't entirely out of the picture, again look at some Italian designs. That's also the layout the SAAB 21 used as well, so it's at the very least worth considering.

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I would leave the SAAB 21 out of this. 239sq ft wing, empty weight 3250kg and loaded weight of 4150kg (clean?) and using a DB 605 engine that weighed 725kg (?).
Rather larger and heavier than the French fighters?
And look at the Italian fighters a little more closely. The 12.7mm guns are heavy but the ammo is about 70% as heavy as the French 13.2 mm per round.
The German cannon is lighter than it appears in most lists. It is ready to go at 42 kg, a 42kg Hispano V still needs a 6-8kg belt feeder or a heavy drum if you don't use the belt feed.
Italians were still doing pretty good.

TM06 said:

The example I used of the 405 is more about the potential to lighten the basic Hispano instead of the 405 itself. Although I do think the 405 could be a reasonable offensive gun, a lighter 404 or some derivative is more probable and would likely show up earlier than the British Mk V.

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Pointing out that while a lighter 404 was certainly possible, it could not be done without sacrificing something. Cutting 40cm off the barrel may not have affected velocity by much and may have helped speed up the rate of fire. Making some of the other moving parts lighter also speeded up the rate of fire. But it also made them less durable/reliable and it might have been a very good trade-off.